This application presents a research program to study the role and mechanisms of apoptosis of T lymphocytes in human immunodeficiency virus-I (HIV-1)infection. Programmed cell death T lymphocytes has been strongly implicated in the pathogenesis of T cell depletion in the acquired immunodeficiency syndrome (AIDS), but how HIV-I induces apoptosis and which cellular mechanisms are involved are still not known. This research program addresses these issues by using a novel retroviral system in which the gene for a cell surface reporter protein, placental alkaline phosphatase (PLAP), is inserted into a replication competent l molecular clone, which permits analysis of infected cells by indirect immunofluorescence and flow cytometry. In addition, a technique for rapidly producing high-titer retroviral stocks allows for infection of a high percentage of cells in culture with recombinant HIV-PLAP. This method also makes it possible to analyze expression of components of the cellular apoptotic machinery in the setting of acute Hw-l infection. Using these techniques, the following specific aims will be addressed: First, does HIV- l predominantly induce apoptosis of infected cells (direct cytopathicity), uninfected cells (indirect killing) or both? Second, which cellular pathways are important in HIV induced apoptosis of T lymphocytes and does viral infection differentially affect the apoptotic machinery in infected versus uninfected cells? Our growing knowledge of the molecular mechanisms of programmed cell death ofT lymph0cytes will be particularly relevant to this issue. Third, which HIV genes are involved in inducing apoptosis? And finally, are there differences between primary viral isolates from patients in different stages of HIV-l infection on induction of apoptosis? This study of apoptosis ofT lymphocytes during HIV-1 infection should shed light on the immunopathogenesis of AIDS as-well as the role of programmed cell death in regulation of the human immune response.